The idea of 'fixing' various traits in an unborn child smacks of science fiction - but in the future, GM technology may allow us to choose the characteristics our children are born with.

The idea of making permanent changes to the human genome attracts both fascination and fear. In fact, doctors are already doing this to some extent, by selecting which babies will be born on the basis of their genetics.

Choosing healthy embryos
In recent years a technique called preimplantation genetic diagnosis (PGD) has been used to screen embryos for several different genetic conditions.
• The main use is to screen for diseases including Huntingdon’s disease, the lung disease cystic fibrosis and more recently Down's syndrome.

The first stage of PGD involves creating embryos by in vitro fertilisation (IVF). A cell is then removed from each of the early stage embryos to identify which ones carry the disease. Only 'good' embryos are placed in the mother’s body to develop.

• Born to help another child
Recently a novel purpose has been found for PGD - to select embryos not for the sake of their own health, but to help a relative.

In 2000 in the United States, the Nash family made medical history by having a baby boy who had been selected using PGD to be a perfect tissue match for their sick older daughter who suffered from a condition called Fanconi anaemia. Donor cells from baby Adam's umbilical cord were successfully used to treat Molly.

The move was highly controversial. It was even said that it paved the way for children to be born to provide 'spare parts'. Even so, the Human Fertilisation and Embryology Authority has given the go-ahead for PGD to be used in similar circumstances in the UK. It is expected that several more children will follow Adam Nash over the next few years.
• Boy or girl?
In some countries, couples desperate for a child of a particular sex can pay thousands of pounds for PGD to ensure they have a child of a particular sex. Using PGD for this purpose is not legal in the UK.


GENETICALLY ENGINEERED HUMANS
If scientists discovered how to engineer your genes to guarantee a life free from cancer, or mental illness, would you want it done? How about athletic ability, or intelligence? It is possible that gene therapy could offer all these enhancements in the future.

Genetically modifying humans
In theory, modifying the DNA of humans could be done in two main ways:
1. The new genes could be put into a fully grown adult. One experimental treatment is aimed at people with cystic fibrosis. They have a faulty gene which results in the production of thick mucous in their lungs. It is not necessary to try to get the new DNA into every cell in their body because the faulty gene only causes damage in certain tissues, so the copies of the gene are sprayed into their lungs to be taken up by cells there.

In the future, however, it might be possible to make genetic changes to a stored supply of human cells outside the body and use these to replace damaged tissue.
2. Alternatively the new genes could be put into a sperm, an egg or an embryo. The embryo would then be transferred to a womb to develop. Making changes to a single cell means that when it divides, it will pass a copy to every new cell. In other words, the person will end up 100% genetically modified and will pass the changes onto their children in their own sperm or eggs. This is called germ line gene therapy and would make a permanent change which would be passed down the generations. For this reason, germ line gene therapy is highly controversial.
Genetically engineered babies might be possible - but experimenting would be too risky

Imagine allowing the first genetically-modified embryo to develop into a person. What would it be like? Would it suffer deformities or would other problems emerge in later life? Most people would find experimenting on babies unthinkable.



However, one of our closest relatives - the rhesus monkey - has already been engineered. Andi the GM monkey was given a jellyfish gene while still an unfertilised egg.

Does this mean humans could be engineered? Perhaps, in the future. At the moment the process is far too inefficient. When Andi was made, hundreds of eggs were wasted, and he was the only one of three monkeys born alive to carry any jellyfish genes. Such wastage could never be allowed to happen in humans